Graphical depiction of a theoretical model of addiction and recovery. (A) In the naïve state, an intrinsic secondary input suppresses craving via an inhibitory pathway. (B) Upon initial exposure to an addictive stimulus, the craving center is further inhibited by the primary pathway resulting in a feeling of euphoria. (C) With continued exposure to the addictive stimulus, the secondary pathway is desensitized by the primary pathway (with possible habituation in the primary pathway not shown), resulting in craving and the onset of addictive behavior. The latter can lead to more craving via a positive feedback vicious cycle as well as mobilization of a tertiary process that can independently perpetuate the addictive behavior. (D) Sudden withdrawal of the addictive stimulus precipitates a state of "cold turkey" characterized by enhanced craving due to the loss of the primary input, continued desensitization of the secondary pathway and continued positive feedback from the addictive behavior. (E) Sustained abstinence will allow resensitization of the secondary pathway and temporary relief of craving. The addictive behavior subsides, but the tertiary process is still lurking and intensifying. Complete rehabilitation to the naïve state (A) calls for extirpation of the tertiary process. (F) Otherwise, reactivation of the tertiary pathway by contextual cues, memory or stress could once again desensitize the secondary pathway, triggering a relapse.